The present invention relates to an established cell line of microglia.
Microglia is cells with macrophage-like properties in the central nervous system, which are cells not only functioning as immunocompetent cells in inflammatory reaction and viral infection and as phagocytes for removing cells but also playing a central role in a cytokine network in the central nervous system (Sawada, M. et al., Int. J. Dev. Neurosci., 13, 253-264, 1995). Recently, the microglia has been revealed to be essential for expression of high-level brain functions such as learning and memorization and considered to be specialized cells having a role specific for the brain.
There are quite a number of hereditary diseases in the nervous system, which occur due to various causative factors, for example by defect of a single enzyme etc. or by unknown reasons. Under these circumstances, supplementary therapy is used to cope with a large number of such disease.
A large number of studies have been made worldwide on the system of selective delivery to the brain. For introducing a gene into the brain in an animal, a method of using neuronphilic viruses as adenovirus vectors is devised, and a system for introducing a gene specifically into neurons is known (Kozarsky, K. F and Wilson, J. M, Curr. Opin. Genet. Dev., 3, 499-503, 1993). A method of using a retrovirus vector is also devised and has succeeded in introducing a gene into hepatic cells. blood cells etc. (Mullingan, R. C., Science 260, 926-932. 1993).
In the brain, however, the blood-brain barrier is present, so it is difficult to conduct supplementary therapy and to introduce an effective drug, and even if a substance (e.g. anticancer drug, DNA etc.) is introduced from a peripheral position, it cannot be introduced specifically into the brain. Therefore, there was no method other than direct injection of the substance by surgical operations.
As a method not involving invasive means such as surgical operations, there is a method of utilizing liposomes, and liposomes rendered capable of introduction into the brain relatively easily by changing their constitutional elements were developed by a Japanese group. However, even in this method too, incorporation of liposomes into the brain is as low as about 1% based on the injection amount, so this method cannot be said to be specific for the brain.
From the foregoing, it is necessary to prepare cells specific for the brain in order to transfer a substance to the brain.
Because microglia is brain cells, it is cited as a candidate for selectively transferring a substance to the brain specifically.
The microglia can be obtained by primary culture of brain cells. For this primary culture, however, the brain should be excised and purified for use, and primary culture usually requires a period of about 2 weeks, so the procedures are cumbersome. Further, the cells are difficult to proliferate during culture and hard to subculture, so after primary culture, it is extremely difficult to introduce a gene into the microglia to express it therein.
The object of the present invention is to provide an established cell line of microglia with specific affinity for the brain.
As a result of their eager study, the present inventors have succeeded in establishing a brain-specific cell line from cells after primary culture from brains of newborn mice and newborn rats, to arrive at the completion of the present invention.
That is, the present invention relates to an established cell line of microglia having the following properties:
(a) form: having a macrophage-like or globular form in the presence of granulocyte-macrophage colony-stimulating factor, and in the absence of said factor, a branched form similar to branched microglia present in the brain, or both of the above forms;
(b) functional characteristics: having specific affinity for the brain, and
having a strong phagocytic ability; and
(c) cell growth ability: growing depending on granulocyte-macrophage colony-stimulating factor.
Further, the present invention relates to an established line of microglia comprising a gene or drug introduced into it.